Ok, seeing as the replies are here I'll continue.
I understand the basic concept that you guys have illustrated but it's when it gets moving like this, taken from
http://www.cardschat.com/poker-odds-expected-value.php:
There are 6 possible clubs that he will call with. So six times, you will win an extra $10. As there are 8 clubs available, the chance of him calling is 6/8 (six out of eight):
$10 * 6/8 = $7.5
If he raises, we know that you have a worse hand, and you will have lost $10.
-$10 * 2/8 = -$2.5
So your expected value of betting here is $7.5 + (-)2.5 = $5. Not bad
It's all to do with card reading and what you think your opponent is likely to do. Now I have a hard enough time guessing whether he will call/raise or fold at all - let alone break it down into percentages of likeliness (35% of the time he will call $10, 45% of the time he will call $5 etc). And that means there is zero chance of being able to break into percentages based on possible cards!